The jury at an inquest in London has found a newspaper salesman was unlawfully killed by a police officer during protests against a G20 conference two years ago.

Ian Tomlinson, 47, a homeless newspaper seller with a history of alcoholism, was walking through a demonstration by thousands of anti-capitalist protesters in London's financial district on April 1, 2009.

Tomlinson was not protesting but kept coming up against police cordons as he tried to make his way home.

One doctor gave evidence that Tomlinson had suffered a heart attack but other experts testified he died from internal bleeding.

Tomlinson collapsed and died minutes after being struck. The incident was caught on video by a passer-by.

The Crown Prosecution Service is now considering criminal charges against the police officer, Simon Harwood, after jurors ruled he acted illegally, recklessly and dangerously.

"We're really grateful the inquest process has made a strong statement about how Ian died," said Tomlinson's stepson Paul King.

"We think the jury finding speaks for itself."

He said the verdict was "a bit of closure for the family".

"It feels like something's being done by some sort of authority and hopefully we'll get the right answers.

"We'd like to go to court and continue with the manslaughter charges."